The importance of few-nucleon forces in chiral effective field theory

TL;DR

This paper emphasizes the significance of including few-nucleon forces at leading order in chiral effective field theory, demonstrating improved descriptions of nuclear systems and suggesting broader implications for many-body physics.

Contribution

It proposes that three- and four-nucleon forces should be included at leading order, leading to more accurate nuclear structure and matter calculations.

Findings

Realistic description of $^{16}$O ground state achieved

LO four-nucleon forces may be crucial for heavy nuclei

Promotion mechanism is general and applicable to other many-body problems

Abstract

We study the importance of few-nucleon forces in chiral effective field theory for describing many-nucleon systems. A combinatorial argument suggests that three-nucleon forces -- which are conventionally regarded as next-to-next-to-leading order -- should accompany the two-nucleon force already at leading order (LO) starting with mass number $A\approx 10-20$. We find that this promotion enables the first realistic description of the $^{16}$O ground state based on a renormalization-group-invariant LO interaction. We also performed coupled-cluster calculations of the equation of state for symmetric nuclear matter and our results indicate that LO four-nucleon forces could play a crucial role for describing heavy-mass nuclei. The enhancement mechanism we found is very general and could be important also in other many-body problems.